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Demand Controlled Ventilation
Demand controlled ventilation (DCV) is a feedback control method to maintain indoor air quality that automatically adjusts the ventilation rate provided to a space in response to changes in conditions such as occupant number or indoor pollutant concentration. The most common indoor pollutants monitored in DCV systems are carbon dioxide and humidity. This control strategy is mainly intended to reduce the energy used by heating, ventilation, and air conditioning (HVAC) systems compared to those of buildings that use open-loop controls with constant ventilation rates. When to use DCV Standard HVAC system design uses fixed airflow rates to calculate the outdoor air (OA) required in a space. These airflow rates are determined by mechanical code and vary based on expected occupancy and space use. This process of supplying fixed airflow to a space ensures that sufficient OA is present in that space when it is occupied. However, such spaces are not always fully occupied; in these cases, ...
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Control Theory
Control theory is a field of control engineering and applied mathematics that deals with the control system, control of dynamical systems in engineered processes and machines. The objective is to develop a model or algorithm governing the application of system inputs to drive the system to a desired state, while minimizing any ''delay'', ''overshoot'', or ''steady-state error'' and ensuring a level of control Stability theory, stability; often with the aim to achieve a degree of Optimal control, optimality. To do this, a controller with the requisite corrective behavior is required. This controller monitors the controlled process variable (PV), and compares it with the reference or Setpoint (control system), set point (SP). The difference between actual and desired value of the process variable, called the ''error'' signal, or SP-PV error, is applied as feedback to generate a control action to bring the controlled process variable to the same value as the set point. Other aspects ...
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Indoor Air Quality
Indoor air quality (IAQ) is the air quality within buildings and Nonbuilding structure, structures. Poor indoor air quality due to indoor air pollution is known to affect the health, comfort, and well-being of building occupants. It has also been linked to Sick Building Syndrome, sick building syndrome, respiratory issues, reduced productivity, and impaired learning in schools. Common pollutants of indoor air include: Passive smoking, secondhand tobacco smoke, Household air pollution, air pollutants from indoor combustion, radon, Mold health issues, molds and other allergens, carbon monoxide, volatile organic compounds, legionella and other bacteria, Asbestos, asbestos fibers, carbon dioxide, ozone and Atmospheric particulate matter, particulates. Source control, filtration, and the use of ventilation (architecture), ventilation to dilute contaminants are the primary methods for improving indoor air quality. Although ventilation is an integral component of maintaining good indoo ...
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Measures Of Pollutant Concentration
Measures of pollutant concentration are used to determine risk assessment in public health. Industry is continually synthesizing new chemicals, the regulation of which requires evaluation of the potential danger for human health and the environment. Risk assessment is nowadays considered essential for making these decisions on a scientifically sound basis. Measures or defined limits include: * ''no-observed-adverse-effect level'' (NOAEL), also called ''no-effect concentration'' (NEC), ''no-observed-effect concentration'' (NOEC) or similarly * ''lowest-observed-adverse-effect level'' (LOAEL) * ''acceptable operator exposure level'' (AOEL) * ECx (in percentage). No-effect concentration ''No-effect concentration'' (NEC) is a risk assessment parameter that represents the concentration of a pollutant that will not harm the species involved, with respect to the effect that is studied. It is often the starting point for environmental policy. There is not much debate on the existence ...
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Heating, Ventilation, And Air Conditioning
Heating, ventilation, and air conditioning (HVAC ) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR (as in the designation of HACR-rated circuit breakers). HVAC is an important part of residential structures such as single family homes, apartment buildings, hotels, and senior living facilities; medium to large industrial and office buildings such as skyscrapers and hospitals; vehicles such as cars, trains, airplanes, ships and submarines; and in marine environments, where safe and Sick building syndrome, healthy building conditions are regulated with respect to temperature and ...
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International Mechanical Code
The International Mechanical Code (IMC) is a consensus national model code concentrating on the installation and safety of heating, ventilation, and air conditioning systems. It is published by the International Code Council (ICC) through a governmental consensus process and is updated on a three-year cycle to include the latest advances in technology and safest mechanical practices. The current version of this code is the 2024 edition. The IMC protects public health and safety for all building heating, cooling and ventilation related design, installation and inspection by providing minimum safeguards for people at homes, schools, and workplaces. Fuel burning appliances, cooling systems, heating systems appliance venting, location and protection of appliances and many other such issues are addressed in the IMC. The IMC is the most widely used mechanical code in the United States and is also used as the basis for the mechanical code of several other countries. See also *Internation ...
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Variable Air Volume
Variable air volume (VAV) is a type of heating, ventilating, and/or air-conditioning (HVAC) system. Unlike constant air volume (CAV) systems, which supply a constant airflow at a variable temperature, VAV systems vary the airflow at a constant or varying temperature. The advantages of VAV systems over constant-volume systems include more precise temperature control, reduced compressor wear, lower energy consumption by system fans, less fan noise, and additional passive dehumidification. Box technology The most simple form of a VAV box is the single duct terminal configuration, which is connected to a single supply air duct that delivers treated air from an air-handling unit (AHU) to the space the box is serving. This configuration can deliver air at variable temperatures or air volumes to meet the heating and cooling loads as well as the ventilation rates required by the space. Most commonly, VAV boxes are pressure independent, meaning the VAV box uses controls to deliver a ...
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Carbon Dioxide Sensor
A carbon dioxide sensor or sensor is an instrument for the measurement of carbon dioxide gas. The most common principles for sensors are infrared gas sensors ( NDIR) and chemical gas sensors. Measuring carbon dioxide is important in monitoring indoor air quality, the function of the lungs in the form of a capnograph device, and many industrial processes. Nondispersive infrared (NDIR) sensors NDIR sensors are spectroscopic sensors to detect in a gaseous environment by its characteristic absorption. The key components are an infrared source, a light tube, an interference (wavelength) filter, and an infrared detector. The gas is pumped or diffuses into the light tube, and the electronics measure the absorption of the characteristic wavelength of light. NDIR sensors are most often used for measuring carbon dioxide. The best of these have sensitivities of 20–50 PPM. Typical NDIR sensors cost in the (US) $100 to $1000 range. NDIR sensors are also used for dissolved for ...
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Variable-frequency Drive
A variable-frequency drive (VFD, or adjustable-frequency drive, adjustable-speed drive, variable-speed drive, AC drive, micro drive, inverter drive, variable voltage variable frequency drive, or drive) is a type of AC motor, AC motor drive (system incorporating a motor) that controls speed and torque by varying the frequency of the input electricity. Depending on its Topology (electrical circuits), topology, it controls the associated voltage or electric current, current variation., quote is per definition on p. 4 of NEMA Standards Publication ICS 7.2-2021. VFDs are used in applications ranging from small appliances to large compressors. Systems using VFDs can be more efficient than hydraulics, hydraulic systems, such as in systems with pumps and damper control for fans. Since the 1980s, power electronics technology has reduced VFD cost and size and has improved performance through advances in semiconductor switching devices, drive topologies, simulation and control techniques ...
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Constant Air Volume
Constant air volume (CAV) is a type of heating, ventilating, and air-conditioning (HVAC Heating, ventilation, and air conditioning (HVAC ) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. ...) system. In a simple CAV system, the supply air flow rate is constant, but the supply air temperature is varied to meet the thermal loads of a space. Most CAV systems are small, and serve a single thermal zone. However, variations such as CAV with reheat, CAV multizone, and CAV primary-secondary systems can serve multiple zones and larger buildings. In mid- to large-size buildings, new central CAV systems are somewhat rare. Due to fan energy savings potential, variable air volume (VAV) systems are more common. However, in small buildings and residences, CAV systems are often the system of choice due to their simplicity, low cost, and reliabi ...
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Carbon Dioxide
Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at normally-encountered concentrations it is odorless. As the source of carbon in the carbon cycle, atmospheric is the primary carbon source for life on Earth. In the air, carbon dioxide is transparent to visible light but absorbs infrared, infrared radiation, acting as a greenhouse gas. Carbon dioxide is soluble in water and is found in groundwater, lakes, ice caps, and seawater. It is a trace gas Carbon dioxide in Earth's atmosphere, in Earth's atmosphere at 421 parts per million (ppm), or about 0.042% (as of May 2022) having risen from pre-industrial levels of 280 ppm or about 0.028%. Burning fossil fuels is the main cause of these increased concentrations, which are the primary cause of climate change.IPCC (2022Summary for pol ...
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ASHRAE
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE ) is an American professional association seeking to advance heating, ventilation, air conditioning and refrigeration (HVAC&R) systems design and construction. ASHRAE has over 50,000 members in more than 130 countries worldwide. ASHRAE's members comprise building services engineers, architects, mechanical contractors, building owners, equipment manufacturers' employees, and others concerned with the design and construction of HVAC&R systems in buildings. The society funds research projects, offers continuing education programs, and develops and publishes technical standards to improve building services engineering, energy efficiency, indoor air quality, and sustainable development. History ASHRAE was founded in 1894 at a meeting of engineers in New York City, formerly headquartered at 345 East 47th Street (the United Engineering Center), and has held an annual meeting since 1895. Until ...
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Room Air Distribution
Room air distribution is characterizing how air is introduced to, flows through, and is removed from spaces. HVAC airflow in spaces generally can be classified by two different types: ''mixing'' (or dilution) and ''displacement''. Mixing systems Mixing systems generally supply air such that the supply air mixes with the room air so that the mixed air is at the room design temperature and humidity. In cooling mode, the cool supply air, typically around 55 °F (13 °C) (saturated) at design conditions, exits an outlet at high velocity. The high-velocity supply air stream causes turbulence causing the room air to mix with the supply air. Because the entire room is near-fully mixed, temperature variations are small while the contaminant concentration is fairly uniform throughout the entire room. Diffusers are normally used as the air outlets to create the high-velocity supply air stream. Most often, the air outlets and inlets are placed in the ceiling. Supply diffusers in t ...
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